This invention relates generally to papermachines and relates, more particularly, to the means and methods for preventing the separation of a paper web from a permeable carrier fabric as the web and fabric are transferred in concert between successive drying cylinders located within the dryer section of a papermachine.
The region of a papermachine with which this invention is concerned involves the inter-cylinder air pocket region located generally between a pair of adjacent drying cylinders and an adjacent turning roll around which a paper web and carrier fabric are moved as the web and fabric are moved through the dryer section of the papermachine. During a paper making operation during which the paper web and fabric are moved around this air pocket region, the paper web and carrier fabric are moved of f of the surface of one of the drying cylinders onto the surface of the turning roll, around the surface of the turning roll and then off of the surface of the turning roll onto the surface of the other of the adjacent drying cylinders.
The turning roll with which this invention is concerned includes an interior which is maintained at a low pressure, or sub-atmospheric, condition by a suitable vacuum source and includes a perforated surface around which the paper web and carrier fabric are moved so that the paper web is exposed to the low pressure condition of the roll interior through the perforations provided in the roll surface and the carrier fabric. The resulting difference in air pressure between the opposite sides of the paper web bias the web against the surface of the carrier fabric and, consequently, against the surface of the turning roll to reduce the likelihood of separation of the web from the fabric as the web and fabric are moved around the surface of the vacuum roll.
In order to reduce the likelihood of separation of the paper web from the run (i.e. the incoming run) of carrier fabric moved from one drying cylinder to the turning roll and from the run (i.e. the offgoing run) of carrier fabric moved from the turning roll to the next, or subsequent, drying cylinder, prior art arrangements have been developed for influencing the internal air pressure of the aforedescribed air pocket region. More specifically, such prior art arrangements are intended to establish and maintain the air pressure within selected areas of the pocket region at a sub-atmospheric condition so that the air pressure on the opposite side, i.e. the web-side, of the fabric/web runs biases the web against the surface of the carrier fabric.
One such arrangement, shown and described in U.S. Pat. No. 4,905,380, utilizes a combination blowbox/vacuum system for inducing a sub-atmospheric condition along the incoming and offgoing runs while advantageously effecting the vacuum capabilities of the turning roll. By comparison, another such arrangement, described in U.S. Pat. No. 5,279,049, relies upon the vacuum-induced sub-atmospheric condition of the interior of the turning roll to bias the web against the carrier fabric as the web/fabric arrangement is moved around the aforedescribed air pocket region. It would be desirable to provide an arrangement for inducing sub-atmospheric conditions within the aforedescribed air pocket region in a manner which, when used in conjunction with the vacuum source for inducing sub-atmospheric conditions within a turning roll, enables the energy requirements of the vacuum source to be reduced to such an extent that the total energy expenditure for satisfactorily biasing the web and carrier fabric against one another as the web and fabric move in concert around the pocket region and the turning roll is reduced.
Accordingly, it is an object of the present invention to provide a new and improved support system and an associated method for reducing the likelihood of separation of the paper web from the carrier fabric as the web and fabric are moved between successive drying cylinders wherein the system and method requires the expenditure of less energy than do prior art arrangements of this class.
Another object of the present invention is to provide such a system which primarily relies upon a blowbox system, rather than the vacuum source associated with the turning roll, for inducing a sub-atmospheric condition along the incoming and offgoing runs of the carrier fabric.
Still another object of the present invention is to provide such a system which requires no contact with moving components of the papermachine, is devoid of mechanical seals, and whose operation promotes cleanliness within the aforedescribed pocket region.
Yet another object of the present invention is to provide such a system which is uncomplicated in construction yet reliable and effective in operation.